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Old Feb 19, 2003, 04:31 AM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
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Bitcharger TX mods

This is the second sticky on the subject of Bitcharger conversions.

The first can be seen here:

Working Bichargers

In this one I'd like people to desribe in as much detail as they can the modifications to the TX they may have done. There are not many so it shouldn't take long.

Please keep your posts concise, if there is any discussion to be done on the issues, can we start other threads to discuss those details.

Next will be the receivers, I'll probably split that up a bit.

Graham
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Old Feb 19, 2003, 08:51 AM
Stuck on a rock
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Germany, NDS, WOB
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My transmitter mod consists of the following:

Use four nicads for extra power. Extend the original aerial to app. 3 times the normal lenght. Rewire the control buttons. No range problems in a big hall/gym.

(and I put it in a cardboard box just to emphasize the cheap concept)

Michael
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Old Feb 19, 2003, 11:34 AM
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I done the 9 volt and voltage regulator mod. Basically You cut the trace which supplies power to your TX2 chip and power it with 5 volts coming from a 7805 Voltage regulator. The 7805 needs 2 capacitors 1 on the input and 1 on the output. Replace the original supply with 9 volts and power the 7805 with the 9 volt also. I got the idea from reading Mr RC Cams website. At first I was using a bad regulator chip and Mr RC Cam helped me figure that out. You can see more details in his thread about bit conversion. I will post a schematic and pic later since Mr RC Cam only has schematics for using the diode regulator.
The mod increased my range from 35-40 ft to 80ft+. That was using stock arials and nicd batteries on rx. Now with lithium polymer battery on Rx along with longer rx arial range is increased further. All this was done on a snow globe type clone.
Be sure to keep your supply wires away from the antenna wires on the inside of the transmitter. It will make things jittery. I mounted my 7805 on the side of the inside of the case.

PS
@epilot
I like your transmitter.
I made some cardboard speaker stands for surround sound.
They looked like square tube rockets , we put collages on from wired magazines(which we could afford with the savings of using cardboard).
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Old Feb 20, 2003, 02:59 PM
Sticky Shepherd
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Any more or is that TX's covered?
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Old Feb 20, 2003, 03:04 PM
Stuck on a rock
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I pretty much think so.

To sum it up:

Add more cells to boost power. If using more than 4 nicads, use a 5 volt regulator for the supply to the TX2 chip - Battery could be a 9volt one.

Extend the antenna to whatever lenght seems to work. No need to get all scientific here.

Rewire the buttons if using the steering channel for motor on/off and the forw/rev control for rudder actuator.

Thats IT!

Michael
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Old Feb 20, 2003, 07:23 PM
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Use a .1uF ceramic on the output and a 1uf electro on the input.
attached are before and after schematics. plus pics of the way I mounted mine.
I edited the pics from RCCams site hope he doesnt mind.







[edit uploaded pictures to here took out comments about ramp up throttle thing no need for that in the tx with the bitsc]
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Old Feb 25, 2003, 05:17 PM
Oxford Panic
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Joined Feb 2003
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Bit-Charger Proportional TX Mods

I originally posted this info in various parts but since then and prompted by some queries I have re-written it to make a little more understandable. As always I have zipped a PDF file and attached it below.

Andy.
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Old Mar 29, 2004, 02:18 PM
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Hi Andy,

I have read your suggestion for pulse control with interest. I have not had time to try it, but I have experimented with a way to perhaps improve the apparent behavior. I found that if you decrease the decode frequency setting resistor on both the transmiter and receiver, you can increase the frame rate by about a factor of three, before the receiver gives up and can no longer decode the signal. This is a very easy thing to try, just reduce the resistor that sets the encoding frequency on the transmitter to about 100kOhm, and make the corresponding resistor on the recevier also about 100kOhm. You have to be careful to make sure the encode/decode oscillators are within 20% of each other, or else nothing will work. If necessary, you need to inrease or decrease one of the resistors some.
You will find that the minimum cycle time for the encoded signal can be reduced to about 300us ( down from the nominal 1ms).
This should give shorter encoded cycles and thus apparent smoother control.

Let me know if you try it whether it makes things smoother.

the resistors in question are between pins 11 and 12 on the transmitter (usually between 180k to 270k standard)
and between pins 4 and 5 on the receiver ( again usually between 180k to 270k standard)

regards,
gerhard
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Old Mar 29, 2004, 04:42 PM
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Gerhard,

That's a new one to me I never heard of that before.
I'll have to try it as this may smooth out the control and get round some of the interaction I found.

The problem with the Rx circuit on the one I used is that it is the type which just has a blob of black epoxy on the PCB so there's no way to count the pins. I do have a circuit diagram so it may be possible to identify it from that.

Thanks,

Andy.
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Old Mar 29, 2004, 05:19 PM
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Hi Andy,

I actually did this experiment with a "blob" type receiver. to find the resistor in question is quite easy. firstly, it is the only resistor in the 180k to 270k range on the board, so if you can read the values, you are good. secondly, if you have an oscilloscope, you can see the oscillator on both pins of this resistor, it's about a few hundred kilohertz, small amplitude. thirdly, here
http://www.hlec.com.cn/pdf/TX-2RX-2.pdf
is a spec with a layout of the I/O pins of die that is under the blob, this helps in guessing which output is where.

let me know how it goes.

Btw, I discovered this quite by accident: I had two different bit cars on the same frequency, but the transmitter from one car would not operate the other car. So I read the part in the spec (see link above) where it stated that the encode and decode frequency must be within 20%. I looked at the encoded signal from the two transmitters (just touch the scope probe to the end of the antenna) and noticed that the encode frequencies were quite a bit off. One was almost twice that of the other. this lead me to try and find out what would be the minimum cycle time that would still work. On my example, the transmitter would encode much much faster that the receiver could keep up. with a 75kOhm resistor on the receiver, and a 250us cycle time, the receiver would sort of work, but very unreliably, sometimes yes, sometimes no. so I backed off a little, and it seems to work ok.

regards,
Gerhard


regards,
gerhard
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Old Mar 29, 2004, 06:06 PM
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Gerhard,

I found a resistor on the Rx board that is 220k as you say there is only one in that range I shall try it with 100k.

Thanks,

Andy.
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Old Apr 01, 2004, 04:57 PM
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Gerhard,

with the higher frame rate you may have an other way to kreate a new kin of "proportional steering" (only theoretic...), older pulse with modulated systems had an frame rate frequency of about 50 Hz. Only the high and the low time of one frame has varys. Maybe now it is possible to rewire the tx switches with some simple electronics. One switch becomes one channel with this theoretical solution. You need an astable multivibrator with a frequency near the new frame rate of the TX (I suggest ca. 40-50 Hz) and an duty cycle of about 50%. Than you have to ad an "half shot" ( 1/2 monoflop) with an pot. now you can vary the duty cycle maybee between 40-60%. Per chanel you need one of each building blocks. After that you have a simple prop. AM RC system. It is only an idea, but it should work...

Jörg
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Old Apr 01, 2004, 05:36 PM
Oxford Panic
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Jörg

A better way of creating proportional control using the bitcharger system would be to generate the signal you need from a PIC controller.

If you go down the analogue route with the switching pulse, which is imposed the original control signal and being close to the same frequency there will be some dreadful aliasing problems to contend with, trust me I ran into this when pulsing the throttle only. I ended up with a pulse rate of about 3Hz. My system interrupts the flow of the encoded signal asynchrously, which means there is a large proportion of unfinished frames that simply don't do anything except get in the way of smooth control. Even though the frame rate is much lower than the pulsing rate during forward only operation the frame rate drops dramatically when steering is applied causing the motor to hiccup as the rates become much closer in frequency. It's just about acceptable the way I have set it up but I must try Gerhard's mods to improve the situation but the best I can hope for once I have upped the frame rate is that the hiccupping will smooth out a bit even if I keep the low speed motor pulsing.

If you could create the codes using a PIC then it may be possible to generate them in the correct sequence without interruption
to get proportional motor and steering but attempting to get both channels proportional using analogue, I think, may not be possible at any acceptable speed.

Andy.
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Old Apr 01, 2004, 08:11 PM
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Jörg, Andy,

One way I can think of that may slightly improve the proportional response without being too complex is to use a PIC based pulser that is synchronized with the transmitter encoder. That is, still use the transmitter’s buttons as inputs, but only change the state of these when the encoded data is in the “W2” mode. You would have to write the code that lets the PIC detect that, and then wait for this state to appear at the transmitter output.
I have observed that the transmitter encoder reacts virtually instantly, i.e. as long as the button is pressed before the actual “W1” frame starts, the encoder will give the code corresponding to the current state of the buttons.

Synchronizing the transmitter encoder thus may improve the proportional response somewhat. It still will suffer from the hugely varying encoded lengths of the different states though.

At what point does one give up and buys a JMP or RFFS?

Regards,
Gerhard
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Old Apr 02, 2004, 11:40 AM
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Andy, Gerhard

an other simple way ist to cut of the TX chip and insert a picc from koichis page to produce an encoded signal, just use the transmitter stage from the bit TX, the chip from ther RX as some amplifcation (OP-Amp?) inputs and outputs. Use them to amplifier the signal and put a pic at the end to decode the transmitted square waves.

If I had tehe chance to programm some pics I would try this way, is there anybode who can help me to get to already programmed ones?
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